Graft scaffold for cartilage repair and process for making same

ABSTRACT

The present invention relates to a method of providing a graft scaffold for cartilage repair, particularly in a human patient. The method of the invention comprising the steps of providing particles and/or fibres; providing an aqueous solution of a gelling polysaccharide; providing mammalian cells; mixing said particles and/or fibres, said aqueous solution of a gelling polysaccharide and said mammalian cells to obtain a printing mix; and depositing said printing mix in a three-dimensional form. The invention further relates to graft scaffolds and grafts obtained by the method of the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 15/535,053,filed Jun. 11, 2017, which is the US National Stage of InternationalPatent Application No. PCT/EP2015/079502, filed Dec. 12, 2015, which inturn claimed the benefit of European Patent Application Nos. 14197449.3,filed Dec. 11, 2014, and 15158224.4, filed Mar. 9, 2015. The contents ofthe foregoing patent applications are incorporated by reference hereinin their entirety.

FIELD

The present invention relates to a three dimensional graft, particularlyfor repair of craniofacial features and injured joints, and to a processof producing patient specific grafts using computer aided modelling andthree-dimensional bio-printing with biocompatible inks.

BACKGROUND

Reconstruction of the nose and external ear in a patient specific mannerare some of the greatest challenges in plastic surgery because of thecomplex, three-dimensional properties of the inner cartilage structurewith regionally changing mechanical properties and overlaying skin.Auricular reconstruction is applicable to congenital deformities,microtia, melanoma related tissue sacrifice and injuries includingaccidents and severe burns. Ears are involved in approximately 90% ofburns involving the head and neck. The mostly frequently used standardtreatment for total auricular reconstruction in the United States andthe European Union is based on a two- to three-stage surgical techniqueusing autologous costal cartilage harvested from the sixth, seventh andeighth rib which is sculpted into an ear-like shape to the extentpossible by the limited amount of harvested tissue. Sufficient amount ofcostal cartilage is generally achieved at age 10, delaying thereconstructive surgery. Another reconstruction method for earreconstructive surgery is the use of silicone implants to avoid the needfor costal cartilage harvesting. However placing an acellular scaffoldunder a thin layer of skin exposes the patient to a high risk oflong-term complications. Additionally, it is impossible to provide forcustomized size and shape for each patient, and the reconstructed eardoes not grow like the contralateral ear leading to asymmetry. Availablereconstruction strategies involve several surgeries and their outcome ishighly dependent of the expertise of the reconstructive surgeon. Donorside morbidity, collapse of the abdominal wall due to lack of costalcartilage support and severe pain related to the costal cartilageharvest are common complications.

Additionally, there is a large clinical need to repair osteochondrallesions, which occur as a result of sport injury, trauma anddegenerative diseases such as osteoarthritis. Current methodologies totreat this involve transplantation of osteochondral grafts, which areeither autologous or derived from bone banks. This treatment has severaldisadvantages including donor site morbidity, scarcity of donor tissue,surgical difficulty and the fact the graft consists of multiple pieces,each which can come loose or be mis-positioned in the height.

In view of this state of the art, the objective of the present inventionis to provide methods and means for providing patient specific graftsthat improve on the above mentioned deficiencies of the state of theart. This objective is attained by the subject matter of the claims ofthe present specification.

SUMMARY

According to a first aspect of the invention, a method of providing agraft scaffold, particularly for use in a human patient, comprises thesteps of:

-   -   providing particles and/or fibres;    -   providing an aqueous solution of a gelling polysaccharide;    -   providing mammalian cells;    -   mixing said particles and/or fibres, said aqueous solution of a        gelling polysaccharide and said mammalian cells to obtain a        printing mix;    -   depositing said printing mix in a three-dimensional form.

According to another aspect of the invention, a method of providing agraft comprises the steps of:

-   -   providing a graft scaffold by the method according to the first        aspect of the invention, or any of its specific embodiments, and    -   depositing said cell-free scaffold into a cell culture medium        comprising mammalian cells, particularly cartilage cells, stem        cells or cartilage precursor cells, in a cell culture step.

According to yet another aspect of the invention, a graft as obtained orobtainable by any of the preceding aspects of the invention, or any oftheir specific embodiments, is provided, particularly for use in amethod for craniofacial or joint repair.

According to yet another aspect of the invention, a method ofcraniofacial or joint repair comprises the computer model of the patientspecific graft modified for three-dimensional additive manufacturingwith cartilage specific printing mix comprising at least onecytocompatible polymer, at least one of minced tissue or other additiveparticle and cells, the crosslinking being provided by spontaneous orexternally triggered reaction of reactive groups and molecules embeddedin the co-extruded material or in bio-ink internally, at least one ofthese types being present on at least one of the polymer, minced tissueand cells to reconstruct functional and native cartilage like tissuegrafts.

According to an aspect of the invention, a method of creating internalpolymer gradients, porosity and support regions for grafts better suitedfor mechanical loading of the tissue graft manufactured is provided byadditive manufacturing methods.

According to an aspect of the invention, a method of creatingsacrificial external support structures to aid in the printing ofoverhanging features of grafts is provided, wherein the sacrificialpolymer is co-deposited with the printing mix and functions as areservoir of crosslinking initiators to polymerize the printing mix andis removed after polymerization.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the invention concerns a method of providing a graftscaffold, particularly in a human patient, comprising the steps of:

-   -   providing an aqueous solution of a gelling polysaccharide;    -   providing at least one of:        -   particles and/or fibres;        -   mammalian cells;    -   mixing said particles and/or fibres, said aqueous solution of a        gelling polysaccharide and said mammalian cells to obtain a        printing mix;    -   depositing said printing mix in a three-dimensional form.

In certain embodiments, the printing mix comprises an aqueous solutionof a gelling polysaccharide and particles. In certain embodiments, theprinting mix comprises an aqueous solution of a gelling polysaccharideand fibres.

Fibres and/or particles, particularly when derived from cartilaginoustissue, may comprise factors aiding in supporting the growth of cellswithin the graft.

In certain embodiments, the printing mix comprises an aqueous solutionof a gelling polysaccharide and both particles and fibres.

In certain embodiments, the printing mix comprises an aqueous solutionof a gelling polysaccharide and cells. In certain embodiments, theprinting mix comprises an aqueous solution of a gelling polysaccharideand cells and one or several growth factors. The inventors havesurprisingly found that even in the absence of cartilaginous particlesor fibres, the provision of gelling material and cells may besufficient, particularly in presence of growth factors, to sustain cellviability and proliferation.

In certain embodiments, the printing mix comprises an aqueous solutionof a gelling polysaccharide and particles and cells. In certainembodiments, the printing mix comprises an aqueous solution of a gellingpolysaccharide and particles and fibres and cells.

In certain embodiments, said particles consist of, or comprise, tissueparticles. In certain embodiments, said particles consist of, orcomprise, cartilage particles. In certain embodiments, said particlesconsist of, or comprise, particles consisting of lyophilized cartilagetissue. In certain embodiments, said particles consist of, or comprise,human cartilage tissue. In certain preferred embodiments, said particlesconsist of, or comprise, autologous cartilage tissue. In certainpreferred embodiments the particles can be clinical products ofmicronized matrix including BioCartilage, Amniofix, Alloderm-Cymetra,Cook Biotech Small Intestial Muscosa (SIS) particles. In certainpreferred embodiments the particles can be hydroxyapatite or calciumphosphate.

In certain embodiments, the particles and/or fibres are made of asynthetic polymer, particularly a polymer selected from the groupconsisting of polymers, or polymers derived from, polyethylene glycol,polypropylene glycol, gel forming poloxamers F108, F127, F68, F88,polyoxazolines, polyethylenimine, polyvinyl alcohol, polyvinyl acetate,polymethylvinylether-co-maleic anhydride, polylactide,poly-N-isopropylacrylamide, polyglycolic acid, polymethylmethacrylate,polyacrylamide, polyacrylic acid, and polyallylamine or co-polymers ofthese or block-copolymers of these.

In certain embodiments, the particles and/or fibres comprise or arepredominantly or exclusively composed of minced tissue. In certainembodiments, the minced tissue is derived from tissue selected from thegroup consisting of auricular cartilage, nasal cartilage, nucleuspulposus, meniscus, trachea, nasal cartilage, rib cartilage, articularcartilage, synovial fluid, vitreous humor, brain, spinal cord, muscle,connective tissues, small intestinal submucosa and liver. In certainembodiments, the minced tissue is in the range of from 5 μm-50 μm,50-200 μm and 200-1000 μm or a combination of these.

In certain embodiments, said gelling polysaccharide is gellan gum,acylated and/or sulfated gellan gum. In certain embodiments, saidgelling polysaccharide is selected from guar gum, cassia gum, konjacgum, Arabic gum, ghatti gum, locust bean gum, xanthan gum, xanthan gumsulfate, carrageen, carrageen sulfate, or a mixture of any of the abovegelling polysaccharides.

In certain embodiments, said solution of a gelling polysaccharidecomprises a cytocompatible polymer as an additive in addition to thegelling polysaccharide, particularly a cytocompatible polymer selectedfrom the group consisting of alginate, alginate sulfate, gellan sulfate,carrageen, carrageen sulfate, guar gum, cassia gum, konjac gum, Arabicgum, ghatti gum, locust bean gum, xanthan gum, xanthan gum sulfate,heparin, fibrin, heparin sulfate, elastin, tropoelastin, chondroitinsulfate, dermatan sulfate, hyaluronic acid, hyaluronan sulfate,cellulose, dextran, dextran sulfate, poly-l-lysine, chitosan, silk andcollagen.

In certain embodiments, the additive is comprised in combination withgellan gum, acylated and/or sulfated gellan gum.

Gellan gum is a water-soluble polysaccharide produced by the bacteriumPseudomonas elodea. The repeating unit of the polymer is atetrasaccharide, which consists of two residues of D glucose and one ofeach residues of L-rhamnose and D-glucuronic acid. The repeat has thefollowing structure:[D-Glc(β1→47D-GIcA(β1→4)Djhbn-Glc(β877→u8ir)L-Rha(α1→3)]_(n)

“Acylated gellan gum” is a term known in the art and refers to gellanthat comprises acetyl in some or all oxygen 5′ positions and glycerylicacid in some of all oxygen 2′ positions of the glucose unit. See FIG. 8:Acylated gellan (A) is a raw product gellan after bacterial fermentationand when it is purified acyl and glyseryl side chains can be cleaved(B). This enhances the gelation and different stiffness can be achieved.Certain embodiments of the present invention combine acylated andpurified gellan together to achieve better flexibility for thestructures.

In certain embodiments, the solution of a gelling polysaccharidecomprises gellan gum or acetylated gellan gum, or a sulfation product ofacylated gellan gum, as the gelling polysaccharide, and alginate,alginate sulfate, gellan sulfate, carrageen, and/or carrageen sulfate asa cytocompatible polymer additive.

In certain embodiments, an aqueous solution of a salt comprisingmonovalent, divalent and/or trivalent cations is added to said gellingpolysaccharide to effect gelation.

In certain embodiments, said aqueous solution comprises between 10 and150 mmol/l of divalent ions. In certain embodiments, said aqueoussolution comprises strontium ions (Sr²⁺). In certain embodiments, saidaqueous solution comprises barium ions (Ba²⁺). In certain embodiments,said aqueous solution comprises calcium ions (Ca²⁺).

In certain embodiments, said aqueous solution comprises a total ofbetween 10 and 150 mmol/l of divalent ions. In certain embodiments, saidaqueous solution comprises between 10 and 150 mmol/l of strontium ions(Sr²⁺), particularly between 15 and 50 mmol/l Sr²⁺. In certainembodiments, said aqueous solution comprises between 10 and 150 mmol/lof barium ions (Ba²⁺), particularly between 15 and 50 mmol/l Ba²⁺. Incertain embodiments, said aqueous solution comprises between 10 and 150mmol/l of calcium ions (Ca²⁺), particularly between 15 and 100 mmol/lCa²⁺.

In certain embodiments, said aqueous solution comprises a total ofbetween 10 and 150 mmol/l of Sr²⁺ and Ba²⁺, particularly between 15 and50 mmol/l of Sr²⁺ and Ba²⁺. In certain embodiments, said aqueoussolution comprises a total of between 10 and 150 mmol/l of Ca²⁺ andBa²⁺, particularly between 15 and 50 mmol/l of Ca²⁺ and Ba²⁺. In certainembodiments, said aqueous solution comprises a total of between 10 and150 mmol/l of Sr²⁺ and Ca²⁺, particularly between 15 and 50 mmol/l ofSr²⁺ and Ca²⁺.

In certain embodiments, said solution of a gelling polysaccharidecomprises a monosaccharide sugar or disaccharide sugar, particularlyglucose, mannose or arabinose, at physiologic osmolarity. This additioncan be important to safeguard viability of the cells embedded in theprinting mix.

In certain embodiments, said particles and/or fibres consist of, orcomprise,

-   -   a biocompatible or cytocompatible polymer, and/or    -   a bioresorbable polymer, particularly a polymer selected from        the group consisting of PLA (polylactic acid or polylactide),        DL-PLA (poly(DL-lactide)), L-PLA (poly(L-lactide)), polyethylene        glycol (PEG), PGA (polyglycolide), PCL (poly-ε-caprolactone),        PLCL (Polylactide-co-ε-caprolactone), dihydrolipoic acid (DHLA),        alginate and chitosan, and/or    -   a synthetic polymer, particularly a polymer selected from the        group consisting of polymers, or polymers derived from,        polyethylene glycol, polypropylene glycol, polaxomers,        polyoxazolines, polyethylenimine, polyvinyl alcohol, polyvinyl        acetate, polymethylvinylether-co-maleic anhydride, polylactide,        poly-N-isopropylacrylamide, polyglycolic acid,        polymethylmethacrylate, polyacrylamide, polyacrylic acid, and        polyallylamine.    -   natural fibers, particularly selected from elastin, resilin, and        silk and their derivatives;    -   A biocompatible conductive material, particularly transition        metal tantalum and conductive polymer polypyrrole (PPy).

In certain embodiments, particles are formed from a biopolymer mentionedabove in oil emulsion or by precipitation. In certain specificembodiments, such biopolymer is alginate.

In certain embodiments, said tissue particles are derived from tissueselected from the group consisting of auricular cartilage, nasalcartilage, nucleus pulposus, meniscus, trachea, nasal cartilage, ribcartilage, articular cartilage, synovial fluid, vitreous humor, brain,spinal cord, muscle, connective tissues, small intestinal submucosa andliver.

In certain embodiments, the cytocompatible polymer is a natural polymer.

In certain embodiments, the cytocompatible polymer is gellan gum ofvarying acylation degree, particularly acylation ranging between 100% to10% acylation, with 100% being high, and optionally comprises anadditive selected from the group consisting of alginate, alginatesulfate, heparin, fibrin, heparin sulfate, elastin, tropoelastin,chondroitin sulfate, dermatan sulfate, hyaluronic acid, hyaluronansulfate, cellulose, dextran, dextran sulfate, poly-l-lysine, chitosan,silk and collagen of varying type and sulfated versions of these.

In certain embodiments, ≥90%, ≥95%, or ≥98% of said particles are in therange of from 5 μm-1000 μm, particularly from 5 μm to 50 μm, 5 μm to 200μm, 50 μm-200 μm or 200 μm to 1000 μm.

In certain embodiments, said fibers are sized in the range of 5 μm-50 μmand 50-500 μm in length having an aspect ratio ranging between 2-1000,particularly an aspect range of 10-500, more particularly 100-500,100-1000, 200-1000 or from 500 to 1000. In certain embodiments, silkfibres are used having a diameter of 1 μm or less, and a length of 500to 1000 μm or more. The aspect ratio for the purpose of the term's usein the context of the present specification is defined as the ratio offiber length to diameter.

In certain embodiments, said mammalian cells are cartilage cells,cartilage precursor cells or stem cells capable of differentiating intocartilage precursor cells or cartilage cells.

In certain embodiments, the mammalian cells are selected from the groupconsisting of primary autologous chondrocytes, primary allogenicchondrocytes, chondroprogenitor cells, chondroblasts, mesenchymal stemcells, induced pluripotent stem cells and adipose-derived stem cells.

In certain embodiments, the printing mix comprises:

-   -   1-6% (w/v), particularly approx. 3% (w/v) of said gelling        polysaccharide;    -   0.5-10% (w/v), particularly approx. 4% (w/v) of said particles,    -   optionally, 0.5-8% (w/v), particularly approx. 2% (w/v) of said        additive.

In certain embodiments, the printing mix comprises:

-   -   approx. 3% (w/v) of gellan gum;    -   approx. 4% (w/v) of cartilage tissue particles,    -   approx. 2% (w/v) of alginate, 10 ng/ml TGBF3    -   10⁶ to 10⁷ cartilage cells per ml.

In certain embodiments, the printing mix is deposited together with asacrificial polymer. This allows the generation of overhangingstructures, such as are especially important in shaping certain featuresof the nose and ear.

In certain embodiments, the printing mix is deposited onto a sacrificialpolymer scaffold.

In certain embodiments, the sacrificial polymer scaffold is co-depositedwith the printing mix.

In certain embodiments, the sacrificial polymer mix and/or scaffoldcomprises divalent cations or other agents of gelation/polymerization.

By diffusing out of the sacrificial polymer mix, into the printing mix,these cations or other agents of gelation/polymerization allow for arapid formation of the three dimensional structure of the scaffold.

In certain embodiments, the three dimensional form and/or saidsacrificial polymer scaffold is derived by 3-D-printing methods,particularly on the basis of a three dimensional computer model of acontralateral organ of said patient.

In certain embodiments, the three dimensional model is obtained bycomputed tomography, magnetic resonance imaging, laser scanning orutilizing three dimensional cameras.

In certain embodiments, the computer model is created to support loadbearing in gradients and to create internal structures for better cellsurvival and porosity.

In certain embodiments, the polymer scaffold is derived by additivemanufacturing methods.

In certain embodiments, the additive manufacturing method is ink jetprinting, bioprinting, extrusion printing or layer-by-layer method.

In certain embodiments, the polymer scaffold is characterized byinternal polymer gradients, porosity and support regions.

In certain embodiments additional polymers are added to increase thematrix liquid viscosity so that the ink can be extruded consistently andis not blocked due to filter pressing phenomena.

In certain embodiments, the sacrificial polymer is removed prior orsubsequent to said cell culture step.

In certain embodiments, the tissue particles and/or bioink comprise agrowth factor or a combination of growth factors, particularly selectedfrom BMP-2, BMP-7, TGF-β1, TGF-β2, TGF-β3, and/or FGF-2, and/ormitogenic factors, particularly IGF-1, to promote healing andregeneration.

In certain embodiments, growth factors can be directly loaded into thebioink mixture. In certain embodiments, the concentration of said growthfactor(s) is in the range of from 0.1-5 mg/ml, 5-50 ng/ml or 50-500ng/ml of one growth factor or a combination of several growth factors.In certain embodiments, the growth factors are selected from BMP-2,BMP-7, TGF-β 1, 2, 3, IGF-1 and/or FGF-2.

In certain embodiments, the printing mix, particularly the particles,comprise additional components, particularly components selected fromgrowth factors, antioxidants, cytokines, drugs and biologics.

In certain embodiments, the sacrificial polymer concludes an agent forinitiating the crosslinking, said agent being a monovalent, divalent andtrivalent cation, enzyme, hydrogen peroxide, horseradish peroxidase,radiation polymerizable monomers such as lithiumphenyl-2,4,6-trimethylbenzoylphosphinate.

In certain embodiments, crosslinking initiating groups are present inthe printing mix, particularly selected from groups that participate inlight exposure, cation-mediated crosslinking and enzyme-mediatedcrosslinking.

Another aspect of the invention concerns a method of providing a graftrepair, comprising the steps of:

-   -   providing a graft scaffold by the method according to any one of        the preceding claims, and    -   depositing said cell-free scaffold into a cell culture medium        comprising mammalian cells, particularly cartilage cells, stem        cells or cartilage precursor cells, in a cell culture step.

Another aspect of the invention concerns a graft scaffold obtainable by,or obtained by, the method according to any one of the preceding methodsof the invention, or any specific embodiment or combination of featuresprovided by the specific embodiments.

The present invention provides patient-specific craniofacialreconstructive grafts produced by additive manufacturing methods. Thecartilage tissue graft abolishes the need for cartilage harvesting thusdecreasing patient discomfort, reducing the surgical time and allowingbetter replication of shape, size and mechanical flexibility.Furthermore faster tissue regeneration and increased cell proliferationcan be achieved to enhance the surgical recovery. For craniofacialapplications this technique can be combined with currently used skinaugmentation treatment (i.e. expanders) or other natural or syntheticskin grafts.

Printing

According to the present invention, patient specific auricular and nasalgrafts are produced based on the three-dimensional scanned models fromthe patient by utilizing additive manufacturing methods such as but notlimited to extrusion printing, inkjet printing and other layer-by-layerdeposition methods. Clinical computed tomography (CT), magneticresonance imaging (MRI) or other three dimensional imaging tools such aslaser scanners, 3D cameras or combinations of these are used to producethe computerized model of the patient specific implant. For earreconstruction, the image can be mirrored to produce a computationalmodel precisely mimicking the contralateral ear for tissue graftproduction. For ear and nose reconstruction a library of graft modelscan be used to provide choice of grafts for the patient especially in acase where a normal contralateral scan cannot be performed. Thesemethods can lead to better cosmetic and aesthetic results when specificsize reductions tools are used to reduce the dimensions of the cartilageframework by the thickness of the skin layer to achieve a final graft ofcorrect size. Additive manufacturing methods can be utilized in creationof these constructs in high precision and in sterile conditions.Furthermore internal support structures and porosity for cell survivalin large constructs can be added in a patient-specific shape and/orstiffness depending on the patient's needs. Avascularized cartilage canbe designed to host vascular structures for over laying skin and othertissues in its proximity to prevent necrosis. The printed cartilageframework can be used as a bioactive template for the construction ofoverlying tissues, releasing growth factors and other secretorymolecules to enhance the viability of neighboring cells. This releasecan be specially designed by having sulfated polymers in the mixture tobind growth factors to the proximity of the cells and slowly releasingthe molecules.

In certain embodiments, the 3D form can be created as a computer modelto support load bearing in gradients and to created internal structuresfor better cell survival and porosity.

The disclosure is further described with reference to the followingfigures and non-limiting examples, which depict particular embodiments.

FIG. 1A is the three dimensional model created based on patient CTmodels and after internal support structure was added for better loadbearing to the graft.

FIG. 1B is a photograph of an intact tissue engineered ear construct.

FIG. 1C is a photograph of internal support that could stabilize the earstructure for more natural like bending properties. Both images B and Cwere fabricated utilizing three-dimensional bioprinting and are composedof minced cartilage particles, gellan gum, and alginate.

FIG. 2 shows graphs illustrating the rheological crosslinking kineticsand the final stiffness of the bioink with two compositions (Bioink, toppanel; Bioink+HA, bottom panel).

FIG. 3 illustrates the time dependency of the mechanical properties withthe 20 mM strontium chloride solution where specimens (n=6) averageultimate stress at failure for each time point was measured in tension(left). Furthermore, the concentration of cations (black=calciumchloride and grey=strontium chloride) has similar effect on crosslinkingdespite the cationic source (right, top and bottom). It can be concludedthat the mechanical properties are highly dependent on the cationconcentration and crosslinking time.

FIG. 4 is a graph illustrating the metabolic activity of thechondrocytes embedded into the printing mix material in printingprocess. Metabolic activity assay (Promega MTS one solution assay wasperformed in several time points analyzed with a plate reader (SynergyH1, Biotek). Positive control was alginate 1% (light gray), printing mixmaterial corresponds to printing mix material without tissue particles(gray) and printing mix material+ECM (dark gray) consists of cartilageextra cellular matrix particles <100 μm in diameter. All conditions wereanalyzed in triplicates.

FIGS. 5A and 5B illustrate the co-deposited support structure providinginitial crosslinking molecules such as cations from any source, enzyme,protein or other activating molecule that initiates the crosslinkingcascade (FIG. 5A) and the final construct with overhanging featuresafter elution of the support (FIG. 5B).

FIG. 6 is a photograph of an intact native size tissue engineered noseconstruct composed of particles, gellan gum, and alginate. Construct wasfabricated utilizing three-dimensional bioprinting in less than 17minutes. Space between the lines represents 1 mm.

FIG. 7 is a bright field microscopy image showing 10% PMMA fiberorientation in 3% gellan gum before shear (left), after uniaxial shearin two directions corner to corner (middle) and after uniaxial shearvertically. Scale bar is 50 microns.

FIGS. 8A and 8B illustrate the gellan gum composition of high acylatedgellan (FIG. 8A) and non acylated gellan (FIG. 8B).

FIG. 9 illustrates the conversion of patient specific three dimensionalmodel during the printing process into tissue engineered nasal graftfrom left to right. Space between the lines represents 1 mm.

FIGS. 10A and 10B show the Fourier transform infrared spectroscopy(FTIR) results of several degrees of sulfation in polymer backbones ofalginate (FIG. 10A) and gellan gum (FIG. 10B). Arrow in 1300 cm⁻¹ marksthe peak of sulfation. In higher degrees of sulfation in polymer thegrowth factor binding is increased leading to better delivery ofmolecules.

FIGS. 11A-11D show the result of a rheological characterization of thebioink compositions with and without particles. Shear thinning wasmeasured in rotation (FIG. 11A), shear recovery in oscillation aftershear of 1 second (100⁻⁸ shear rate) for two cycles (FIG. 11B), Bioinkalone was ionically crosslinked with several cation conditions (FIG.11C), and maximum storage modulus G′ of the samples crosslinked for 30minutes with 20 mM SrCl₂ (FIG. 11D). Error bars represent standarddeviation.

FIGS. 12A-12D show the result of a determination of the tensile andswelling properties of the printed constructs. Tensile testing wasperformed on printed dumbbell specimens where the nozzle path is shownby the black lines and the printed structure is shown after swelling(FIG. 12A). Representative stress-strain curves where failure occurredin the central region of the specimen (FIG. 12B). Swelling behavior ofthe bioink compositions based on equation (2) and (3) to evaluate totalwater retention (FIG. 12C) and water retention after crosslinking (FIG.12D) respectively. The smallest divisions on the ruler are 1 mm anderror bars represent standard deviation.

FIGS. 13A-13C show the result of a determination of cell viability ofprinted constructs and the cell proliferation assay. Viability afterprinting one layer thick discs was evaluated with live dead staining(FIGS. 13A and 13B) where 80% viability was observed 3 h after printing,which recovered to 97% by day 4. To assess viability in a largestructure, a young adult size nose was printed and the viability wasevaluated from a central slice (diffusion distance ˜5 mm) evaluated bylive dead staining. A cell viability of 60% was observed. Scale bar 5 mm(FIG. 13B, left), and 50 μm (FIG. 13B, right). Additionally, cell numberin casted disks were evaluated with DNA quantification (FIG. 13C) wherea statistically significant increase in DNA from day 1 to day 21 wasobserved with Bioink+Cartilage particles and both TGF-β3 supplementedcompositions. Error bars represent standard deviation and level ofsignificance was (p<0.05).

DETAILED DESCRIPTION

Material

The bioink material comprises at least one cytocompatible polymer and atleast one of particles and cells, the crosslinking being provided byspontaneous or externally triggered reaction of reactive groups andmolecules, at least one of these types being present on at least one ofthe polymer, minced tissue and cells. The cytocompatible polymers(hereinafter referred to as “the polymers”) for use in this method maybe any suitable polymers with the necessary cytocompatibility, that is,their presence is not harmful to cells. They may be natural(biopolymers) or synthetic materials, or combinations of these. Thenecessary reactive groups allowing the crosslinking may be alreadypresent on the polymers, or the polymers may be modified to include suchgroups. Typical non-limiting examples of natural polymers includealginate, alginate sulfate, heparin, fibrin, heparin sulfate, elastin,tropoelastin, chondroitin sulfate, dermatan sulfate, hyaluronic acid,hyaluronan sulfate, cellulose, dextran, dextran sulfate, poly-l-lysine,chitosan, gelatin, gellan gum of varying acylation degree, gellansulfate, guar gum, cassia gum, konjac gum, Arabic gum, ghatti gum,locust bean gum, xanthan gum, xanthan gum sulfate, carrageen, carrageensulfate, silk and collagen of varying type. All sulfated versions ofthese polymers are included.

Typical non-limiting examples of synthetic polymers include, but are notlimited to, polymers, or polymers derived from, polyethylene glycol,polypropylene glycol, polaxomers, poly oxazolines, polyethylenimine,polyvinyl alcohol, polyvinyl acetate, polymethylvinyl ether-co-maleicanhydride, polylactide, poly N-isopropylacrylamide, polyglycolic acid,poly methylmethacrylate, polyacrylamide, polyacrylic acid, andpolyallylamine.

By “at least one” of the groups being present on at least one of thepolymer, particles and cells, is meant that the added reactive groupsmay be present on all or any of these entities.

Particles incorporated to polymer solution can consist of but are notlimited to extracellular matrix tissue particles, loaded or unloadedbeads and fibers in size range between 5-500 microns.

Crosslinking

The formation of hydrogel based on the material combination, particlesand cells can be initiated by many factors or agents, including but notlimited to mono-, di-, trivalent cations, enzymes and radicalinitiators. Additionally, physical and physical-chemical methods may beemployed, for example, treatment in low or high pH solution anddifferent temperature regions during the manufacturing process.

In certain embodiments, either one of said printing mix and said polymerscaffold comprises reactive groups covalently attached thereto,particularly reactive groups facilitating linking of said printing mix,or its constituent components, to said particles, by crosslinking byspontaneous or externally triggered reaction, wherein reactive groupsare present on at least one of the polymer, minced tissue and cells toreconstruct functional and native cartilage like tissue grafts.

Particles

The size of the minced tissue to be used may be any suitable size, butin a particular embodiment, it is from 5 microns-500 microns, so that itcan be extruded without clogging the dispensing unit such as needle orvalve. The minced tissue for use in the method may be any suitabletissue, but it is advantageously tissue of a similar or identical natureto that of the cartilage. Exemplary and non-limiting examples ofsuitable tissue include articular cartilage, nucleus pulposus, meniscus,trachea, nasal cartilage, rib cartilage, ear cartilage, synovial fluid,tracheal cartilage, vitreous humor, brain, liver, spinal cord, muscle,connective tissues and subcutaneous fat, intrapatellar fat pad, smallintestinal submucosa. A particular example is tissue with high contentof elastin and glycosaminoglycan, particular examples being any type ofcartilage, nucleus pulposus and meniscus. The tissue may be minced byany suitable method, exemplary and non-limiting methods includinghomogenizing, cryomilling, dry milling, cutting, chopping, crushing andslicing. The tissue may be subject to decellularization to removeepitopes which can cause acute inflammatory responses and pathogensincluding HIV. Recently, decellularized tissues, that is, tissue inwhich the cells have been killed and their remnants removed, haveattracted interest as scaffold material alternatives to simplerapproaches where the scaffold is composed of a single material (Hoshibaet al. “Decellularized matrices for tissue engineering”. Expert Opinionon Biological Therapy. 2010; 10:1717-28). Tissue decellularizationresults in a scaffold of extracellular matrix ideally suited forregenerating injured or diseased tissue since it retains the highresolution architecture and biological cues necessary for recapitulationof function. Decellularization may be done, for example, by usingdetergents, hydrogen peroxide, sodium hydroxide and enzymes, RNase andDNase. Particles can be manufactured by methods such as but not limitedto colloid formation by hydrophilic/hydrophobic interactions, two phaseemulsions and in oil interfaces. Fibers can be manufactured by methodssuch as but not limited to electrospinning, fiber extrusion and fiberpulling. Particles and fibers of any kind may be minced by any suitablemethod, exemplary and non-limiting methods including homogenizing,cryomilling, dry milling, cutting, chopping, crushing and slicing. Theseadditive tissue pieces, particles and fibers may be further modifiedwith functional groups binding to carrier polymer or combination ofthese materials or treated to expose reactive groups for crosslinking.Furthermore growth factors, antioxidants and drug molecules may beloaded in or on the added polymers, tissue pieces, particles and fibers.

Cells

The use of the term “cells” in this description encompasses not onlyindividual cells, particularly mammalian cells, more particularly humancells, most particularly autologous human cells, but also encompassesagglomerations of the described cells which form spheroids, pellets, andmicrotissues, which are well known to and commonly used by the art. Thecells for use in the method are advantageously cells of a similar typeas those present on the cartilage tissue. Typical non-limiting examplesof suitable cell types include primary autologous chondrocytes, primaryallogenic chondrocytes, chondroprogenitor cells, chondroblasts,mesenchymal stem cells, induced pluripotent stem cells andadipose-derived stem cells, neural crest derived stem cells.

Printing Mix Material

The term “printing mix” in the context of the present specificationrefers to an extruded mass comprising the key constituent components:

-   -   Particles made of natural (optionally: dried) tissue or fibre,        or made of biocompatible, optionally bioresorbable, polymer, or        both polymer and natural tissue/fibre,    -   An aqueous solution of a gelling polysaccharide, particularly        gellan gum or a derivative thereof, and    -   Mammalian cells.

The composition of the printing mix material may be varied across a widerange, depending on the nature of the materials and the end-use. Thepolymers are typically present in a weight proportion of from 0.5-20%.When minced tissue, particles or fibers are present, they are typicallypresent at a weight proportion of from 10-40% of dry polymers or equally1-20% in total weight. When cells are present, they are typically usedat concentrations of 3×10⁶ cells/ml-50×10⁶ cells/ml.

In addition to the major components hereinabove described, thecrosslinkable material may include other materials, present to conferparticular properties on the material. One particular example iselastin, which is abundant in auricular and nasal ECM to provide theelasticity of the tissue and other examples include growth factors,cytokines, drugs, biologics, siRNA, DNA, antioxidants such aspolyphenols into the polymeric solutions, which could augmentregeneration of the tissues. Added growth factors could be bound tosulfated polymers or unmodified polymer for enhanced delivery andeffectivity in the proximity of the cells residing in the printing mix.

The printing mix material in its ready-to-use form is a readilythermally gelled state that can easily be applied to take desired shapein the manufacturing process. Powders of the molecules and lyophilizedminced tissue, particles and fibers can be stored and sterilizedseparately. All the components can be combined before packaging orrehydrated just prior to use thus preserving the growth factors andproteins for long periods of time.

Shape

Patient specific tissue grafts are tailored for each patient or certainmodel catalogs can be created for situations where patient imaging isnot desired or not possible. The three-dimensional model obtained fromexternal ear and nose scans can be modified to contain internal supportstructures, gradient of polymers for versatile mechanical properties andporosity for enhanced cell survival in large constructs. Furthermoreregion could be tuned in terms of stiffness, growth factor cocktail andconcentration, for example, to induce regional variations in cellproliferation. For example the periphery of the cartilage graft could bemore porous or softer allowing more nutrient flow into the deepstructure. Also the regional specificity and tissue types are found inthese constructs, for example, in the lobe of the ear fat is the maintissue and is responsible for the mechanical properties. The regionalproperties and specified structures can be easily built in alayer-by-layer manner. In such a layered approach, the crosslinkingmechanism would take place not only within individual layers, but alsobetween adjacent layers, thus forming a completely integrated continuousstructure. This can be achieved by initiating crosslinking in theperiphery of the construct in contact with support structure containingthe reactive molecule reservoir.

Support

Support structure can be co-deposited with the printing mix material tosupport overhanging structures, to initiate crosslinking or to preventdrying of the material during deposition. Support material can containcrosslinking factors including but not limited to mono-, di-, trivalentcations, enzymes and radical initiators. Additionally, physical andphysical-chemical methods may be employed by support materialinteractions to modify the pH and molecule concentration. After theconstruct manufacturing the support structure can be eluted. Elution canbe due to but not limited to temperature change, pH change or degradingmolecules.

The result is a cartilage repair that is quick, effective andlong-lasting. The longevity is an important factor in the graft topreserve the mechanical properties until sufficient ECM production ofthe cells has been achieved to produce a native cartilage-likestructure.

Typical examples of the use to which the method of this disclosure maybe put include:

-   -   Reconstruction of craniofacial defects;    -   Filling and reconstruction partial tissue loss and integrating        them with native tissue;    -   Reconstruction of trachea (windpipe), meniscus or costal        cartilage with patient specific grafts;    -   Filling of osteochondral defects

The method of the invention is characterized by the followingadvantages:

-   -   Possibility to produce patient specific tissue grafts for        craniofacial and orthopaedic applications such as but not        limiting to: ear, nose, articular cartilage.    -   Possibility to tune the bending properties to match the scaffold        with physiological parameters and specific regions of the native        tissue.    -   Possibility to include functional load bearing regions of more        compact polymers and reinforced structures to tune the        mechanical properties of the graft.    -   Provides better patient satisfaction and decreased pain levels        due to elimination of the need for cartilage harvest.    -   Utilizes autologous, allogenic or xenogenic native tissue which        already contains the complex array of tissue-specific        extracellular matrix components in physiologically accurate        proportions. These particles are mainly responsible of the        proliferation cues stimulating the chondrocytes.    -   Tissue fragments from any possible ECM particles can be        incorporated into hydrogel blend for additive manufacturing        purposes to produce any desired geometry without compromising        its biochemical composition thus rising prospects for organ        bioprinting.    -   Possibility to incorporate therapeutic factors within the        scaffold including, but not limited to: pharmaceutical        compounds, growth factors, peptides, proteins, carbohydrates,        and gene therapy vectors. Additionally, homing molecules can be        included that would induce host cell migration into the        scaffold.    -   Possibility to achieve zonal organization of tissue architecture        by layering various tissues/compositions using additive        manufacturing techniques.

EXAMPLES Example 1a: Bioprinting of Patient Specified Tissue Wafts

Clinical computed tomography imaging was performed and the resultingcomputational three-dimensional object (FIG. 1) was obtained. Thepatient specific external ear model was then mirrored for thecontralateral side and a new 3D model was generated. Together with thenew model the external support structure model was generated to supportthe ear structure especially in the overhanging regions during theprinting. Support structure was designed to be in contact with the inkin the strategically important places to initiate the crosslinking andto support the overhanging features (FIG. 5). The co-extrusion of thesupport material was shown to preserve horizontal bioink lines withoutsagging and the printed shape accurately after elution of the support.Furthermore the internal support structure of more dense polymers wasprepared to allow better force distribution in internal structure (FIG.2, 3). All models were converted into machine code in STL-converter(RegenHU) and transferred into the bioprinter (BioFactory, RegenHU) forthe printing process.

Using the same technique the inventors have demonstrated the printing ofseveral cartilaginous structures including meniscus, intervertebraldiscs and nose. Two-component intervertebral disc grafts could beprinted with two bioink compositions mimicking the nucleus pulposus andthe annulus fibrosus.

Example 1b: Production of Cartilage Particles for Three-DimensionalPrinting Purposes

Cartilage was harvested from the fresh bovine articular or auricularcartilage by removing thin layers of cartilage into a petri dishcontaining PBS and penicillin-streptomycin 1%. The harvested cartilagewas transferred into cryomill (Retsch) and milled for three cycles in 30Hz intensity. Milled cartilage was collected and lyophilized to obtaindry powder that could be sieved into the desired particle size range.These particles can be further loaded with growth factors or othermolecules to enhance the proliferation and other cell responses. Afterloading the particles were lyophilyzed and cryopreserved to maximize thebiomolecule availability for prolonged shelf life.

Example 1c: Printing Mix Material Preparation and the Printings Process

Printing mix material (“Bio-Ink”) was produced by combining gellan gumin 3.5% concentration with the alginate 3%. Gellan gum was dialyzedagainst ultrapure water to minimize the cation residues in the material.Dialysis was performed over three days in 70-80° C. ultrapure waterchanging the water one to two times a day. Gellan was furtherlyophilized to obtain a dry powder. Purified gellan gum was dissolvedinto glucose containing deionized water making it more cell compatibleand alginate solution was added to obtain final concentration ofpolymers. The polymer blend was mixed with ECM particles and 6×10⁶cells/ml to obtain the final printing mix material. This printing mixmaterial stimulated the cell proliferation significantly compared topositive control (FIG. 4). Cartilage extracellular matrix production wasevaluated with histology and immunostaining after 8 weeks in culture forBioink alone and Bioink+ECM with and without growth factor TGF-β3. TheBioink+ECM without growth factors stimulated cell proliferation aboveBioink alone which was clearly visible in H&E staining. TheBioink+Cartilage particles showed a slight increase in Alcian bluestaining and a slight collagen II staining was observed suggesting theneed for additional growth factor stimulation. Cells were often seenproliferating around the particles without growth factor whereas theBioink+Cartilage particles with TGF-β3 had no site-specificproliferation which suggests that the particles are a source ofmitogenic growth factors. After 8 weeks, the gross appearance of thescaffolds suggested that the growth factor stimulation had a cleareffect on cartilage matrix production as seen in the size and opaqueappearance of TGF-β3 supplemented samples. Both supplemented bioinkcompositions showed a significant increase in cartilage ECM componentsand had areas which began to resemble the cell density and GAG contentof native cartilage. Furthermore, collagen II deposition was strongthroughout the graft in the growth factor supplemented conditions whileonly pericellular staining was seen in the samples cultured withoutTGF-β3. Collagen type I and alizarin red staining were performed todetermine the fibrocartilage production and calcification. Collagen Iwas found in Bioink+Cartilage particles and in both TGF-β3 supplementedconditions suggesting some fibrocartilage production, perhaps due to thepassaging of the cells. In all the conditions calcification was absentsuggesting the cartilage phenotype of the chondrocytes was stable.

The printing mix material was printed onto a substrate and the supportpolymer Pluronic F127 was co-extruded to fill subsequent layer. Pluroniccontained 20 mM of SrCl₂ to initiate the bioink crosslinking uponcontact with the ink. Cations diffused into the printing mix materialdue to osmotic balance and electrostatic forces which initiated thecrosslinking. Structures were generated with 410 μm needles and 800mm/minute feedrate. Pressure applied to extrusion syringe varied between1.2-1.4 bar. After layer-by-layer deposition of the material intodesired form, the sacrificial support Pluronic was eluted in a 20 mMSrCl₂ bath for few minutes before the construct was transferred to 37°C. cell culture medium. FIG. 1 illustrates the ear cartilage internalsupport structure and FIG. 6 shows the nose grafts generated by thistechnique. FIG. 2 illustrates the initial storage modulus being 100 kPaafter crosslinking which is comparable to high stiffness hydrogels.

Example 2: Bioink Composition Optimized for its Mechanical Propertiesand Growth Factor Retention

Bioink preparation: Gellan was added to D-glucose (300 mM) containingultra-pure water at 90° C. to achieve a 3.5% solution, of which 85% waslow-acyl gellan gum and 25% was high-acyl gellan gum. Alginate was addedto the mixture to achieve 2.5% solution. The boiling flask was kept at90° C. with agitation until the solution was homogeneous, typically forone hour. The homogeneous solution was cooled down to 30° C. prior thecell mixing. Briefly, the bovine chondrocytes (4×10⁶ cells/a) were mixedin the DMEM solution and added to the bioink in culture medium in 1:10volume ratio to pre-crosslink the bioink. Mixing was performed until thesolution reached room temperature and the printing syringes were loaded.

Gellan gum high acyl (GG-HA) and low acyl (GG-LA) compositions (FIG. 8)contribute to the stiffness and the elasticity of the final bioink. Byvarying the ratio between the acylation forms the materials cancrosslink tighter yielding stiffer matrix whereas by disrupting thetight packing of the polymer chains in crosslinking more elastic matrixcan be produced. These parameters were optimal for craniofacialapplications in 85% GG-LA, 25% GG-HA composition which provides tunablecrosslinking properties up to 230 kPa ultimate stress and an averagestrain of 68% at failure (FIG. 3). To further optimize the growth factorretention in the bioink a concentration of 2% of sulfated gellan gum(GG-3%) (FIG. 8) was added to the bioink. This composition was superiorin retaining the loaded growth factors, in this case TGF-β3 and FGF-2,in the bioink compared to the non-sulfated bioink.

Example 3: Optional Printing Material and Crosslinking Process withSupport Material

Base polymer gellan 3% with additive hyaluronan conjugated with tyramine3% were mixed together to generate enzymatically crosslinkable hydrogelin the presence of horseradisch peroxidase (HRP) and hydrogen peroxide.Materials were dissolved into deionized water in presence ofmonosaccharide glucose in physiologic osmolarity, specifically 300 mM.Hydroxyapatite particles in concentration of 4% (w/v) were added to thepolymer mixture. This bio-ink composition was further bioprinted in thepresence of HRP and hydrogen peroxide when HRP was mixed either to thebio-ink in 1 unit/ml concentration or to the pluronic F127 30% mixturetogether with the hydrogen peroxide in 0.0012% concentration.Layer-by-layer constructed scaffold crosslinked immediately upon contactwith the support structure. The support structure was eluted in the coldmedium to decrease the negative effects of hydrogen peroxide in thepresence of the cells. The structure was washed several times after tominimize the amount of hydrogen peroxide residues.

Example 4: Fiber Reinforced Materials for Bioprinting

Gellan 3% was dissolved in deionized water and 10% (w/v) polymethylmetacrylate (PMMA) fibers were added as chopped eletrospun fibers intothe gellan solution. Fibers were imaged with scanning electronmicroscopy to determine the fiber diameter to be approximately 2 micron.The fiber reinforced gellan was imaged before the shear (FIG. 7 left)and after two different shear orientation for 2 minutes (FIG. 7 middleand right). Fiber orientation was greatly increased in uniaxially shearalready after 2 minutes. Furthermore, the uniaxial but notunidirectional shear oriented the fiber shorter than 50 microns to sheardirection, thus allowing us to form heterogeneous load bearingstructures in the matrix. However, fibers longer than 50 microns werenot able to keep the orientation in shear when direction of shear wasaltered. During the extrusion printing the shear pattern is uniaxial andunidirectional in the nozzle, thus orientating the fibers to flowdirection. Upon fast cessation of flow we can keep the fiber orientationuniaxial which will affect the load bearing capability of thestructures. These structures are nature inspired and for examplecollagen II fibers in articular cartilage are changing the orientationin different cartilage layers.

Example 4a Bioink Crosslinking

An exemplary bioink is a blend of gellan and alginate mixed with humanmicronized Cartilage particles or HA particles (≤40 μm size). Uponaddition of mono-, di- or trivalent cations, gelation (sol-geltransition) occurs as the helices aggregate into junction zones whichare linked into a three dimensional network via the coiled part of themolecule. The printing process is divided into three stages namelybioink pre-printing, printing process and post-printing crosslinking.Initially the bioink was loaded into a syringe and the support polymerinto a second syringe. At this stage, a small amount of cations werepresent in the bioink to increase viscosity and enhance printingproperties. During the printing process the co-extruded of the support,cations diffused to the periphery of the printed structures to initiatethe crosslinking. After the final structure is completed, the supportcan be eluted in 4° C. cation-supplemented medium.

Example 4b: Rheological Analysis

The cation related viscosity enhancement and crosslinking properties canbe investigated with rheology and mechanical testing. Rheologicalproperties of the Bioink, Bioink+HA, and Bioink+Cartilage Particles weremeasured with an Anton Paar MCR 301 (Anton Paar, Zofingen, Switzerland)rheometer to determine the shear behavior and shear recovery. All of thebioink compositions showed shear thinning behavior which is critical forextrusion (FIG. 11 a). Furthermore, all the compositions had a yieldpoint (weak gel formation) prior to extrusion which is important inpreventing particle and cell sedimentation in the syringe (Table 1).

TABLE 1 Summary of the rheological measurements. The yield points werecalculated using the Herschel/Bulkley equation. Bioink + CartilageBioink Bioink + HA Particles Yield point 15.6 Pa ± 17.7 Pa ± 122 Pa ±0.7 Pa 6.5 Pa 22 Pa Cessation 21% 90% 98% in 10 s* Maximum 152 kPa ± 110kPa ± 96 kPa ± G′ 3.0 kPa 2.0 kPa 1.0 kPa *Shear recovery at 10 s afterthe 2nd shear sequence.

The shear recovery curves (FIG. 11b ) illustrate the recovery of thebioink structure after the printing process. Shear recovery after thesecond shear sequence was 98% in Bioink+Cartilage Particles and 90% inBioink+HA after ten seconds. At the same time the Bioink alone recoveredto only 21% of the original modulus. FIG. 11c illustrates the storagemodulus G′ after cation-induced crosslinking of Bioink alone where thecation concentration and source had a clear influence. FIG. 11dillustrates the final storage modulus for the three bioink compositions.The Bioink alone had the highest final storage modulus (152 kPa±3 kPa)compared to Bioink+Cartilage Particles (96 kPa±1 kPa) and Bioink+HA (110kPa±2 kPa), suggesting that crosslinking is somewhat hindered by theparticles irrespective of their source.

Example 4c: Mechanical Properties and Swelling Behavior

Mechanical properties of the bioprinted cartilaginous structures wereassessed in tension. Tensile dumbbell specimens were printed usingBioink+HA particles with or without cells. The nozzle path (printingdirection) in the gage section of the specimen was chosen to be parallelto the direction of tension (FIG. 12a ). Young's modulus wassignificantly higher in acellular constructs (E=230 kPa±7.0 kPa)compared to cellular ones (E=116 kPa±6.8 kPa) (p<0.001), suggesting thatthe cells increase the compliance of the construct and/or inhibit thecrosslinking. There was no difference in failure strain between theacellular (37%±6.4%) and cellular (34%±2.1%) (p=0.54) constructs.

Swelling of the bioink with and without particles was quantified toassess the total water retention and the water retention after gelcrosslinking (FIG. 12c-d ). Swelling at 37° C. up to 48 hours increasedthe hydrogel weight between 2000-3800% of the dry weight of the samplewhich is typical of hydrogels and between 26% and 54% of thecrosslinking weight of the hydrogels. Fully hydrated state was achievedafter 24 hours and in more specific the Bioink and Bioink+Cartilageparticles were fully hydrated after 5 hours suggesting faster swellingkinetics. Comparison between swelling ratios of the Bioink alone and theparticle containing compositions after 48 hours suggested dependency onthe particle type.

Example 4d: Bioink Compatibility

Cellular bioprinting process was investigated with Bioink+HA to excludeall the interactions and proliferation cues between particles and cells.One layer thick discs were printed to assess the cell viability afterprinting (FIG. 13a ) which was compared to the initial viability of thecells prior to mixing. To investigate cell viability in largestructures, a young adult sized nose (3.1 cm, 2.6 cm and 1.5 cm) wasprinted and kept in static culture until the cell viability in themiddle of the construct was evaluated from a central slice (minimumdiffusion distance of 5 mm). Bioprinting with the particles showed an80% viability three hours after printing, however, after four days thecell viability recovered to 97% where it remained until the end of theexperiment. The young adult sized nose graft had decreased viability inthe center of the scaffold (60% viable cells at day 7) compared to 96%viability in the periphery (FIG. 13b ). This suggests the need forincorporating internal porosity or channels to enhance nutritiontransport. By introducing interconnected porosity into 1.5 cm high cubesthe viability in the center of the structure was as high as in theperiphery. Such nutrition channels ^([)or engineered porosity can beincorporated into the bioprinted structures by extruding the supportpolymer within the grafts, which could later be cleared in subsequentwashing/crosslinking steps. With this technique a complex 3Dinterconnected porous network can be created that is used to perfuse thegrafts with nutrient-rich medium. To further enhance mass transport ofnutrients, grafts can also be pre-conditioned in dynamic bioreactors.

The effect of cartilage particles and growth factor, in this caseTGF-β3, supplementation on cell proliferation was evaluated in castedgels cultured for 21 days. The Bioink alone did not stimulate cellproliferation; in fact there was a loss in DNA at day 7 which slowlyrecovered. Bioink+Cartilage particles, on the other hand, stimulatedproliferation and caused a statistically significant increase (p<0.001)in DNA over 21 days. With TGF-β3 supplementation, there was astatistically significant increase in DNA in the Cartilage particlescontaining samples at day 7 (p<0.001). By day 21, both bioinks showedincreases in DNA, which were not statistically significantly from eachother.

Example 4e: Extracellular Matrix Production and Cartilage Formation

Cartilage extracellular matrix production was evaluated in bioink aloneand bioink+Cartilage particles with histology and immunostaining after 3and 8 weeks in culture. Histological evaluation after 3 weeks revealed aclear increase in cell number, GAG synthesis and collagen II productionin both bioink compositions supplemented with TGF-β3 (10 ng/ml).Furthermore, Bioink+Cartilage particles without growth factorsstimulated cell proliferation above Bioink alone which was clearlyvisible with 3 and 8 week H&E staining. At both time points theBioink+Cartilage particles showed a slight increase in Alcian bluestaining and at the 8 week time point a slight collagen II staining wasobserved suggesting the need for additional growth factor stimulation.Cells were often seen proliferating around the particles without thegrowth factor supplementation which suggests that cell-particle adhesionand/or growth factors in the particles are important. However, becausein the Bioink+Cartilage particles with TGF-β3 samples, no site-specificproliferation was observed, the results suggest rather the particles area source of mitogenic growth factors and not specific cell-matrixadhesive cues. After 8 weeks, the gross appearance of the scaffoldssuggested growth factor stimulation had a clear effect on cartilagematrix production as opaque appearance and increase in size wasobserved. At 8 weeks, both supplemented bioink compositions showed asignificant increase in cartilage ECM components and had areas whichbegan to resemble the cell density and GAG content of native cartilage.Furthermore, collagen II deposition was strong throughout the graft inthe growth factor supplemented conditions while only pericellularstaining was seen in the samples cultured without TGF-β3. Collagen I wasfound in Bioink+Cartilage particles and in both TGF-β3 supplementedconditions suggesting some fibrocartilage production, perhaps due to thepassaging of the cells. In all the conditions calcification was absentsuggesting the cartilage phenotype of the chondrocytes was stable.

Example 4f: Magnetic Resonance Imaging

To assess the shape retention of the printed structures several MRItechniques were evaluated. The printed nose was kept in PBS for 2 weeksto assure complete swelling prior T2-weighted MR imaging. These imageswere thresholded and converted into a .STL file and compared to theoriginal model used for printing and to the cartilaginous graftimmediately after printing. Comparison of the original model and theprinted graft illustrates precise material extrusion and detailedstructures. However, slightly thicker nostril walls were observed incomparison to the original model. Furthermore, when comparing theprinted structure to the MRI model after 2 weeks swelling, a slightthickening of the nostril walls were observed, however, no sign ofdegradation or deterioration of the shape was detected.

Example 5: Bioprinting Process Parameters

One important factor of the reproducible printing process is theconnectivity of the consecutive lines. In order to assess the effect ofline spacing an optimization of line thickness must be conducted.Printing parameters such as pressure, feed rate and needle diameter weretested to standardize the line thickness to 900 μm±53 μm. After thedetermination of the average line thickness the effective line-lineadhesion was investigated by printing a series of tensile testingdumbbells having different line spacing. The dumbbells were tensiletested until failure and the data illustrates that by increasing theline spacing the possibility of defects in the structure increasedsuggesting that in order to provide reproducible mechanical propertiesfor printed structures the lines should overlap approximately 40-50%.The data suggested that the variance of the ultimate stress at failuredid not differ in the tested samples with amount of overlapping linesdown to 20% whereas the number of samples that were not stabile enoughfor testing increased with increasing line spacing. According to thedata the optimal line spacing is affected by the bioink in questionhowever by increasing the overlapping the probability of internalprinting process related defects decreases. Furthermore the linethickness can be freely chosen by changing the process parameters suchas pressure, printing speed and needle diameter.

Several mechanical testing measurements were performed for the newlydesigned bioink to investigate the parameters affecting thereproducibility of the structural and mechanical properties. The tensileevaluation of specimens printed with varying printing directions andwith cell laden bioink revealed that the youngs modulus, ultimate stressand the failure strain are not altered by adding of the cells in theseeding density of 4×10⁶ illustrating that the volume fraction of cells(—1% approx.) is compensated by the strong surrounding matrix.Furthermore, dumbbell specimens were printed in varying printingdirections with respect to the tension, namely parallel to tension (0°),perpendicular to tension(90°) and in 45° angle to the tension (45°). Theprinting direction did not show any statistically significantdifferences between the groups suggesting that the bioprinted structurescan be designed based on the printing and process related parametersrather than based on the estimated mechanical loading of the finalstructures.

We claim:
 1. A graft scaffold obtainable by, or obtained by a methodcomprising: providing an aqueous solution of a gelling polysaccharideselected from the group consisting of gellan gum, acylated and sulfatedgellan gum; providing at least one of: particles and/or fibres andmammalian cells; mixing said aqueous solution of a gellingpolysaccharide, said particles and/or fibres, and/or said mammaliancells to obtain a printing mix; and depositing said printing mix in athree-dimensional form, wherein said solution has a concentration of 1%to 6% (w/v) of said gelling polysaccharide, wherein said solution of agelling polysaccharide further comprises alginate; and wherein the graftscaffold comprises a) said gelling polysaccharide; b) at least one ofsaid particles and/or said fibers and/or said mammalian cells; and c)alginate.
 2. The graft scaffold of claim 1, wherein said solution has aconcentration of 3% to 3.5% (w/v) of said gelling polysaccharide.
 3. Thegraft scaffold of claim 1, wherein the alginate concentration is 2.5% or3% (w/v).
 4. The graft scaffold of claim 1, wherein said gellingpolysaccharide is acylated gellan gum.
 5. The graft scaffold of claim 1,wherein said aqueous solution of a gelling polysaccharide furthercomprises between 10 and 150 mmol/l of divalent ions.
 6. The graftscaffold of claim 1, wherein both mammalian cells and at least one ofparticles and fibres are provided for obtaining said printing mix. 7.The graft scaffold of claim 1, wherein only mammalian cells are providedfor obtaining said printing mix.
 8. The graft scaffold of claim 1,wherein said solution of a gelling polysaccharide further comprises amonosaccharide sugar or disaccharide sugar at physiologic osmolarity. 9.The graft scaffold of claim 1, wherein a growth factor and/or amitogenic factor is provided within the printing mix.
 10. The graftscaffold of claim 9, wherein the growth factor or mitogenic factor isselected from the group consisting of BMP-2, BMP-7, TGF-β1, TGF-β2,TGF-β3, FGF-2, and IGF-1.
 11. The graft scaffold of claim 9, wherein theconcentration of growth factors is 0.1-5 ng/ml, 5-50 ng/ml or 50-500ng/ml.
 12. The graft scaffold of claim 1, wherein said mammalian cellsare cartilage cells, cartilage stem cells, or cartilage precursor cells.13. The graft scaffold of claim 1, wherein said mammalian cells arepresent at concentrations of 3×10⁶ cells/ml-50×10⁶ cells/ml.
 14. Thegraft scaffold of claim 1, wherein said printing mix comprises 10 ng/mlTGF beta
 3. 15. The graft scaffold of claim 1, wherein depositing saidprinting mix in a three-dimensional form is performed by deposition oflines of said printing mix, wherein each line has a width of 700 to 1100μm and said lines overlap by 20% to 60%.
 16. The graft scaffold of claim1, wherein said depositing is performed by 3-D-printing methods.
 17. Thegraft scaffold of claim 1, wherein said depositing is performed byadditive manufacturing methods.
 18. The graft scaffold of claim 17,wherein the additive manufacturing method is ink jet printing,bioprinting, extrusion printing or layer-by-layer method.
 19. The graftscaffold of claim 1, wherein the 3-Dimensional form is generated basedon a computer model of a contralateral organ of said human patient.